So even though I have searched walkthroughs and wikis, i cant seem to find this particular quest, I beleive because it isn't actually a quest but possibly an achievment??? I have rescued the deputy and I am in the position of installing a new sheriff at Primm. Problem is that I came across a mine and a little tooltip notified me I have found 4 / 24 mines . As I said, I googled this and it seems that if you don't clear the mines at some point during a quest , someones going to walk over a mine and die.. Obviously I don't want that to happen so I am setting about trying to find them. I have only found one which was on a destroyed bridge with a single plank of wood to cross the chasm and an ncr checkpoint with a guard on the other side.. that's literally the only one i found myself.
no locations on google that i can find, just a few mentions of the quest here and there.